1. Technical Field
This invention relates in general to improvements in the field of magnetic disk drive systems which are also known as direct access storage devices (DASD), and are commonly referred to as disk drives. More particularly, this invention relates to a method and apparatus for attaching an individually and independently insertable and removable self-locking actuator arm in an actuator am assembly in a disk drive system.
2. Description of the Background Art
One of the most common methods of storing information at the present time is to utilize magnetic disk drive systems. Disk drive systems store information on tracks of rotatable magnetic recording disks. The disk drive industry has been driven by a continuing objective of producing magnetic disk drive systems of higher storage capacity in a given size known as "form factor". At the same time, the industry has been driven by the need to decrease the size of the disk drives, provide faster response time, and lower the cost of the disk drives.
One approach to increase the storage capacity of the disk drive is to increase the number of disks. However, as the number of disks increase, the physical height of the disk drive increases as well. Such an increase in height of a disk drive cannot be accommodated in a given form factor. To maintain the form factor and increase the number of disks at the same time, one must reduce the spacing between the disks. However, the space between each pair of disks in a given disk stack must be sufficient to accommodate an actuator arm (also referred to as mounting arm or arm) and one or two head suspension assemblies (also referred to as head gimbal assemblies which consist of heads mounted to a flexure) which are attached to the actuator arm. Therefore, the disk drive industry has been engaged in finding ways to reduce the disk to disk spacing by decreasing the thickness of the actuator arms, the size of head suspension assemblies, and the material and methods used to attach head suspension assemblies to an arm.
There are a number of methods which are commonly used in the disk drive industry to attach a head suspension assembly to an actuator arm to make an actuator arm stack. They are ball swaging, welding, bonding, bolting, and screw in. Although all these methods are well developed and are being used at the present time, when disk to disk spacing falls below 1.5 mm, ease of assembly, reworkability, and reduction of the components' size becomes crucial and in this regard, all these methods of attachment become impractical.
For example, the ball swaging technique involves swaging a spud made of a hard material into an actuator armhole where the actuator arm is made of a soft material. During this process, a hard ball enlarges the spud cylinder thus forcing the outside surface of the spud cylinder into the inside surface of the actuator arm hole causing the outside surface of the spud cylinder to deform into the inside surface of the actuator arm hole. However, in order for this method to work effectively, the arm must be thick enough to have sufficient rigidity and strength to withstand this attachment process. Furthermore, the thickness of the arm must be sufficient to accommodate the height of the spud. These requirements directly limit how thin an actuator arm can be made which consequently limits how far disk to disk spacing can be reduced.
Another common method is to use one or more screws to attach the head suspension assembly to an arm. However, this method also suffers from several drawbacks such as (1) additional space required to accommodate the screws; (2) additional cost associated with screws; and (3) added manufacturing process.
U.S. Pat. No. 5,062,018 shows a swaged head arm mounting arrangement consisting of an E-block actuator with a plurality of platforms (actuator arms) and plurality of flexure arms (load beams) where a shape-memory alloy material, preferably in a form of a coupling tube, is used to attach the flexure arms to their associated platforms. In this type of attachment, however, in order to insert or remove any flexure arm from its associated platform, freon has to be sprayed into the tube to transform the tube to its martensitic phase and then withdraw the tube.
U.S. Pat. No. 5,132,857 shows a head carrier for carrying a plurality of head/arm assemblies where the head carrier provides the head/arm assemblies with the correct orientation for assembly to the actuator mechanism of a disk file. Here the head carrier loaded with the head/arm assemblies is presented to the actuator so that the bevelled tail portion of each arm locates in a corresponding slot, which comprises two "V" shaped grooves in facing side members in the actuator mechanism. In this type of attachment, however, once the arm is in place, clamping bolts are necessary to secure the head/arm assemblies.
U.S. Pat. No. 4,943,875 shows a head/arm assembly where a mounting band is used to secure the head suspension assembly to an actuator arm. In this design, the arm has to be made from a very rigid material so it can withstand mounting and dismounting of the band. The requirement for rigidity limits how thin the actuator arm can be made. Furthermore, the disk to disk spacing has to be wide enough to further accommodate twice the mounting band thickness. This dependency further limits how far disk to disk spacing can be reduced.
U.S. Pat. No. 5,313,355 shows a flexure mounting scheme for hard disk drives where flexure is attached to a mounting plate by welding. The mounting plate has a pair of legs which engage with a pair of slots formed in the lateral surfaces of an actuator arm. However, in this scheme, the disk to disk spacing is limited by the height of the arm which in turn is directly proportional to the size of the slots.
Examples of other means and methods of attaching head suspension assemblies to an actuator arm are further shown in the following references: European Patent Application 438,806, published Jul. 31, 1991; U.S. Pat. No. 5,187,626, issued Feb. 16, 1993; U.S. Pat. No. 4,947,275, issued Aug. 7, 1990; U.S. Pat. No. 5,097,588, issued Mar. 24, 1992; U.S. Pat. No. 5,146,450, issued Sep. 8, 1992; U.S. Pat. No. 4,698,709, issued Oct. 6, 1987; U.S. Pat. No. 5,012,367, issued Apr. 30, 1991; U.S. Pat. No. 4,893,205, issued Jan. 9, 1990; IBM Technical Disclosure Bulletin Vol. 29, No. 1, June 1986, p. 256; IBM Technical Disclosure Bulletin Vol. 32, No. 8A, Jan. 1990, p. 71; IBM Technical Disclosure Bulletin Vol. 30, No. 11, April 1988, p. 397.
As disk to disk spacing becomes smaller, the actuator arms must be made thinner which means conventional methods of attaching head suspension assemblies to actuator arms becomes impractical. The actuator arm can be made very thin if the head suspension assembly is permanently bonded or spot welded to the actuator arm. Bonding or spot welding is a very desirable method of attachment. However, if head suspension assemblies are permanently attached to the actuator arms, then under the current actuator designs where actuator arms are an integrated part of an actuator, the complete actuator assembly has to be discarded even if a single head suspension assembly is defective or damaged. This would be prohibitively expensive. Therefore, an invention is needed to provide substantial reduction in disk to disk spacing in disk drive systems and at the same time provide a low cost method and apparatus for individually repairing and replacing head suspension assemblies.